The present invention relates generally to manufacture of materials such as nano-sized structures. More particularly, the present invention provides a method and structure for fabricating a nanotube based structure comprising an electrical shortening technique and mechanical forming technique to manufacture carbon based nanotube structures having a desired length. Merely by way of example, the invention has been applied to an atomic force microscope, but it would be recognized that the invention has a much broader range of applicability. For example, the invention can be applied to fluorescent atomic force microscope, commonly called FANSOM, other instrumentation, electronic devices, biological devices, and others.
Over the years, significant development of different types of microscopy has occurred. As merely an example, visible light optical microscopy using far field optics including lenses and light evolved from a simple compound microscope that is capable of resolving sizes of about 200 nanometers and greater. Examples of samples that are capable of being viewed using far field optics include biological cells and tissues, and others, which are often, bulk in nature. The resolving ability of such far field optical microscopy is generally limited by the diffraction of light. The diffraction limit for optical resolution has been stretched somewhat for far field imaging of very specific samples to perhaps 150 nanometers using confocal microscopes and other, related, approaches. Accordingly, atomic force microscopes (“AFM”) and scanning optical microscopes including near field scanning optical microscopes were developed. The AFM and near field scanning optical microscopy (“ANSOM”) have been developed to overcome certain limitations of far field optics. The AFM and near field scanning microscopes have also found many applications in biology, chemistry, physics, and materials science.
Near field scanning optical microscopy allows one to take optical images with resolutions below the diffraction limit of light. More particularly, light propagating through a waveguide is forced through a subwavelength aperture, which is then scanned in close proximity to a sample. Such subwavelength aperture techniques create other limitations. Here, physical limitations relate to a skin depth of the metal used to coat the waveguide and various scanning artifacts, which yield resolutions of 30 to 50 nanometers, most typically 50 to 100 nanometers. Apertureless near field scanning microscopes have been proposed and demonstrated to overcome these limitations, among others. Conventional ANSOM often involves using an oscillating sharp probe, which is scanned over the sample. The probe perturbs an incident laser beam, by introducing phase shifts in an electric field or by a periodic occlusion of the sample. Detection techniques are generally used to discriminate light scattered by near field interactions from a far field contribution. Limitations also exist with such ANSOM techniques. Such limitations include contaminated images based upon certain artifacts of the sample topography, and may include others.
A pioneering approach for achieving high resolution spectroscopic information using a scanning microscope is described in U.S. Pat. No. 6,002,471, assigned to California Institute of Technology, Pasadena, Calif., and in the name of Stephen R. Quake (“Quake”). Quake generally provides a system and method for obtaining high resolution spectroscopic information. The system generally includes a support and first optical elements for directing an optical beam at a sample, which is on the support. An optical element for collecting light emitted from the sample to reduce a background noise is also included. Other elements include a spectral dissociating apparatus, a probe, and a probe detection apparatus coupled to the probe. Although significant advances have occurred, certain limitations still exist with these conventional approaches.
Certain advances in technology have occurred with the probe design for conventional ANSOM and FANSOM designs. Such advances have relied upon single wall carbon nanotubes (“SWNTs”). Most particularly, single-wall carbon nanotubes have shown potential as high-resolution scanning microscopy probes. This includes, though is not limited to, application as high-resolution AFM imaging probes. A level of resolution possible for both single molecule imaging and force transduction in AFM is generally limited by size of the structure of the tip. Conventional silicon-based probe tips have radii of curvature of 5–15 nanometers Unfortunately, conventional silicon-based tips are often delicate, leading to substantial variations in tip shape and size even between successive images. SWNTs, on the other hand, have diameters between 1.5 and 6 nm, providing resolution comparable to molecular scale dimensions. Carbon nanotubes are also chemically and mechanically robust, with axial Young's moduli of about 1.25 TPa, resulting in a tip structure that is stable over prolonged imaging periods. SWNTs can be chemically functionalized uniquely at their very ends, permitting a broad array of applications in nanotechnology and biotechnology. Nevertheless, conventional carbon based nanotubes have limitations. That is, carbon based nanotubes are often difficult to reproducibly assemble in large quantities of high-quality single-wall nanotube AFM tips. These and other limitations are described throughout the present specification and more particularly below.
From the above, it is seen that improved high resolution scanning techniques are desired.